Electrochemical Nuclear Magnetic Resonance Research Articles

Compact In Situ Electrochemical NMR with Wireless and Anti-interference Strategy in Multiscenario Applications.

The integration of electrochemistry with nuclear magnetic resonance (NMR) spectroscopy recently offers a powerful approach to understanding oxidative metabolism, detecting reactive intermediates, and predicting biological activities. This combination is particularly effective as electrochemical methods provide excellent mimics of metabolic processes, while NMR spectroscopy offers precise chemical analysis. NMR is already widely utilized in the quality control of pharmaceuticals, foods, and additives and in metabolomic studies. However, the introduction of additional and external connections into the magnet has posed challenges, leading to signal deterioration and limitations in routine measurements. Herein, we report an anti-interference compact in situ electrochemical NMR system (AICISENS). Through a wireless strategy, the compact design allows for the independent and stable operation of electrochemical NMR components with effective interference isolation. Thus, it opens an avenue toward easy integration into in situ platforms, applicable not only to laboratory settings but also to fieldwork. The operability, reliability, and versatility were validated with a series of biomimetic assessments, including measurements of microbial electrochemical systems, functional foods, and simulated drug metabolisms. The robust performance of AICISENS demonstrates its high potential as a powerful analytical tool across diverse applications.

In situ monitoring multi-carbon alcohol oxidation by combined electrochemistry with spatially selective NMR spectroscopy

In situ electrochemical nuclear magnetic resonance (EC-NMR) plays a pivotal role in electrochemical observation on liquid fuel cells, but its applications are generally trapped by insufficient spectral resolution caused by spatiotemporal variations of magnetic fields. Herein, we develop a general spectroelectrochemistry protocol to address this problem and facilitate real-time electrooxidation analyses. This protocol enables the direct extraction of well-resolved and undistorted NMR signals from standard NMR instruments, thus it is commonly applicable to in situ electrochemical studies. The effectiveness for electrooxidation mechanism investigations on multi-carbon alcohols is validated by 1-butanol electrooxidation. It is verified that the direct oxidation of 1-butanol to butyric acid becomes more significant along with higher potentials on Pt/C at 60 °C, while 1-butanol oxidation is more likely to yield gaseous products (mainly CO2) at lower potentials. Additionally, this protocol reveals that Pt/C rather than PtRu/C is inclined to accomplish the β -C–H bond breaking process for CO2 generation at a high potential of 1.2 V (vs. SCE) . Therefore, this study provides a promising paradigm for electrooxidation investigations on fuel cells, and it may take a meaningful step toward wider electrochemical studies and NMR applications.

Experimental and Computational Study on SEI Composition and Electrochemical Performance of Lithium-Ion Battery with Silicon Oxide-Graphite Composite Electrode

Demand on batteries with high energy density is surging. Conventionally, carbon materials have been used as an anode active material, but recently silicon materials are likely to be incorporated to form a composite anode in lithium-ion batteries (LIBs) for higher energy density. However, LIBs which include silicon materials in anode tend to show a low cycle performance especially the ratio of silicon materials in the anode increases. Commercial LIBs still have difficulty in incorporating large amount of silicon materials especially under the requirements where multiple aspects like safety, charging rate and energy density should be totally met.One potential pathway to improve the cycle performance in LIBs with silicon materials is to tune the nature of solid electrolyte interphase (SEI), a thin film which forms at the interface between anode active material and electrolyte. The nature of SEI is particularly important for LIBs with silicon materials because such silicon active materials show large volume changes during battery operation and SEI is dynamically reconstructed. It has been qualitatively reported so far that LiF is an important component for better battery performance. Our work suggests that the ratio of LiF in initially formed SEI is a crucial factor to realize improved cycle performance in such LIBs.In our work, anode with silicon oxide (SiOx)-graphite composite is considered. We investigated the relationship between electrochemical performance of the cell with such composite electrode and the nature of the film estimated by characterization and molecular simulation. We systematically changed the composition of liquid electrolyte to form various types of SEI on anode surface. For characterization, both fresh and aged cells with different electrolytes were dismantled, and SEI components were extracted by designated solvents, then NMR (nuclear magnetic resonance) was applied to identify the SEI species and quantify the amounts of major SEI components. Comparison between the evolution of SEI amount and an impedance element in electrochemical impedance spectroscopy during aging indicates that degradation of the cells is closely related to the growth of SEI. To further deepen understanding the role of LiF, molecular dynamics simulation was carried out, where the mixture of LiF and typical organic SEI was modelled. Correlation between calculated mechanical property and measured electrochemical performance of the cells were revealed. In our presentation, the requirements that SEI should satisfy will be discussed from the insight of electrochemical measurements, NMR characterization and modeling approaches.

Reversible lithium insertion and conversion process of amorphous VS4 revealed by operando electrochemical NMR spectroscopy

Due to the high theoretical capacity, VS4 is a promising electrode material for next-generation rechargeable batteries. In this study, the lithium insertion and conversion process of amorphous VS4 was investigated using operando electrochemical nuclear magnetic resonance (NMR) spectroscopy. Amorphous VS4 has a chain-like structure similar to that of crystalline VS4. The chain structure was drastically changed to the [VS4]3− tetrahedral structure by lithium insertion up to the Li3VS4 composition. The lithium insertion into the [VS4]3−-based structure proceeded further up to the Li6VS4 composition, with charge compensation by the reduction of the V valency. Finally, the conversion reaction from amorphous Li6VS4 to metallic V and 4Li2S was observed. The structural reversibility of amorphous VS4 was confirmed after the delithiation. It is worth mentioning that the delithiation process from the conversion products was different from the lithiation, resulting in a relatively large voltage hysteresis. Broadly, this study demonstrates that the operando electrochemical NMR technique is a useful tool for investigating the complex reaction system of non-crystalline battery materials.

In Situ Real-Time Quantitative Determination in Electrochemical Nuclear Magnetic Resonance Spectroscopy

For the purpose of acquiring highly sensitive and differential spectra in in situ electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy, uniform distributions of amplitudes and phases of radio frequency (RF) fields in the sample are needed for consistent flip angles of all nuclei under scrutiny. However, intrinsic electromagnetic incompatibility exists between such requirements with electric properties of the conductive material in an electrolytic cell, including metallic electrodes and ionic electrolytes. This proposed work presents the adverse repercussions of gradually varying electrolyte conductivity, which is strongly associated with the change of ion concentrations in a real-time electrochemical reaction, on spatial distributions of RF field amplitude and phase in the detective zone of an NMR probe coil. To compensate for such a non-linear trend of the spatial dependent distribution, we eliminate different excitation effects of the RF field on the build-in external standard and the electrolyte both situated in nearly the same detection area, as well as promote the greater accuracy of quantitative determination of reactant concentrations. The reliability and effectiveness of the improved in situ EC-qNMR (quantitative NMR) method are confirmed by the real-time monitoring of the electrochemical advanced oxidation process for phenol, in which instant concentrations of reactants and products are detected simultaneously to verify the degradation reaction scheme of phenol.

Boosting C3-alcohol electrooxidations by co-fueling with formic acid: A real-time quantitative nuclear magnetic resonance spectroelectrochemical study

C3-alcohols can theoretically provide high current efficiencies in direct fuel cell applications because of their intrinsically large energy densities. However, during realistic reactions, molecular multiple carbon–carbon (CCC) bonds are hardly broken, severely reducing current efficiencies. Herein, directly with commercial Pt/C as the catalyst, the operation of co-fueling with formic acid significantly enhances the current efficiencies of two types of C3-alcohols, namely, isopropanol and 1,2-propanediol. Compared with the current densities of pure C3-alcohols, those of co-fueled C3-alcohols increase maximally by 9.9 times. The reason lies in the fact that the co-fueling design facilitates the breaking of CCC bonds, as elucidated by charge distributions that are obtained via electrochemical nuclear magnetic resonance analyses. Density-functional-theory computational results indicate that the generation of OH groups adsorbed on Pt surfaces is promoted in co-fueling experiments, reducing energy barriers for breaking progress. The co-fueling strategy is capable of optimizing C3-alcohol electrooxidations in direct fuel cells and deserves extensive study.

Understanding the Electrocatalytic Solid-Liquid Interface: The Early Years of the Więckowski University of Illinois Research Group

Andrzej Więckowski was an Assistant/Associate Professor of Chemistry at the University of Illinois Urbana-Champaign from 1985 to 1996 and a Full Professor from 1996 to 2012. Andrzej had a unique ability to attract students to his research group due to his infectious enthusiasm, boundless energy, and excitement for science and cutting-edge experimental approach. This talk will focus on the early years of Andrzej’s tenure at the University of Illinois and his pioneering research in probing the composition and structure of electrocatalytic solid-liquid interfaces using ultra-high vacuum techniques (Figure 1), radiochemistry, and electrochemical nuclear magnetic resonance spectroscopy.Figure 1. (left) The first ultra-high vacuum instrument in the Andrzej Więckowski University of Illinois, Urbana-Champaign research group and (right) Andrzej, 1987. Figure 1

MoS2 nanoflower supported Pt nanoparticle as an efficient electrocatalyst for ethanol oxidation reaction

Developing highly active and stable ethanol oxidation electrocatalysts is crucial for direct ethanol fuel cells. Herein, platinum/molybdenum disulfide nanoflower (Pt/MoS2) nanocomposite is synthesized through a facile method and is first applied as catalyst for ethanol oxidation reaction. In situ electrochemical nuclear magnetic resonance is carried out to investigate the electrocatalytic activity of Pt/MoS2 and the detailed mechanism of ethanol oxidation reaction. Experimental results indicate that in situ electrochemical nuclear magnetic resonance possesses great advantages for real-time investigation of ethanol oxidation reaction, and Pt/MoS2 is found to exhibit better electrocatalytic performances in terms of higher current density, better stability, and stronger anti-poisoning activity compared to commercial Pt/C and pure Pt catalysts in acid electrolyte, suggesting its potential for application in direct ethanol fuel cells. Density functional theory calculations indicate that MoS2-supported Pt atom has a smaller energy barrier for the dissociation of ethanol compared to those of Pt and C-supported Pt atom, leading to the enhancement of catalytic activity. This work reveals the importance of the supporting materials for high performance direct ethanol fuel cells catalysts.

Versatile, Robust, and Facile Approach for in Situ Monitoring Electrocatalytic Processes through Liquid Electrochemical NMR Spectroscopy.

With the strength of liquid nuclear magnetic resonance (NMR) to noninvasively and specifically realize the structural elucidation and quantitative analysis of small organic molecules, in principle, liquid in situ electrochemical-NMR (EC-NMR) possesses great advantages for detecting dissolved species during the electrochemical process. However, the intrinsic incompatibilities between the coupling techniques as well as the sophisticated setups modification still limit the applications toward a wide range. To overcome these bottlenecks, herein we propose an easy-to-construct design with good compatibility and presenting improved electrochemical and NMR performances. As proof of concept, model experiments of alcohol electrooxidation were performed to confirm the capacity of this device for liquid in situ EC-NMR study. The temporal evolution of both the product and the current distributions can be reliably recorded to aid mechanistic and kinetic understanding of electrocatalysis. The depiction of the selective electrooxidation reveals the surface structure-catalytic functionality. This work demonstrates the universality and effectivity of the proposed platform to develop the liquid in situ EC-NMR technique as a useful tool for the dynamic analysis of electrochemical processes at a molecular level.

In Situ Stripline Electrochemical NMR for Batteries

AbstractSome long‐outstanding technical challenges exist that continue to be of hindrance to fully harnessing the unique investigative advantages of nuclear magnetic resonance (NMR) spectroscopy in the in situ investigation of rechargeable battery chemistry. For instance, the conducting materials and circuitry necessary for an operational battery always deteriorate the coil‐based NMR sensitivity when placed inside the coil, and the shape mismatch between them leads to low sample filling factors and even higher detection limits. We report, herein, a novel and successful adaptation of stripline NMR detection that integrates seamlessly NMR detection with the construction of an electrochemical device in general, or a battery in particular, which leads to an in situ electrochemical NMR technique with much higher detection sensitivity, higher sample filling factor, and which is particularly suitable for mass‐limited samples.

In Situ Battery Spectroscopy: A Novel Approach to Investigate Unmodified Working Batteries

We develop a new system and capability for performing in situ electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy on batteries with the aim to measure spectroscopic data during battery cycling. In traditional battery NMR, the battery under investigation is placed inside a solenoid coil. The metal battery electrodes, essential to the battery operation, are necessarily also placed inside the coil, which lowers the sensitivity and resolution of the resulting data. In the case of electrodes that are thick compared to the radiofrequency skin depth at the NMR frequency, in situ NMR may be impossible. In that case, the rf field is effectively screened by the metal electrodes and is prevented from imparting the magnetic energy necessary for NMR to the interior of the battery. Our system, in contrast, uses an internal stripline detector. The essential 2-dimensional stripline detector is built into the battery itself during fabrication, and allows high quality NMR data to be obtained in situ during battery operation regardless of the thickness of the electrodes. Initial 7Li NMR results on pouch cell batteries with a variety of cathode materials (LiFePO4, LiCoO2, and LiNi5Mg3Co2O2) versus a graphite anode are discussed. The EC-NMR system can be used to study any NMR active nucleus of interest and so is versatile in studying a variety of battery types. This technique has the potential to allow investigation of many poorly-understood battery chemistries, and provides the means to monitor the creation and consumption of chemical species during actual battery operation conditions. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This work was funded by the Sandia Exploratory Express LDRD program.

A novel in situ electrochemical NMR cell with a palisade gold film electrode

In situ electrochemical nuclear magnetic resonance (EC-NMR) has attracted considerable attention because of its ability to directly observe real-time electrochemical processes. Therefore, minimizing the incompatibility between the electrochemical device and NMR detection has become an important challenge. A circular thin metal film deposited on the outer surface of a glass tube with a thickness considerably less than the metal skin depth is considered to be the ideal working electrode. In this study, we demonstrate that such a thin film electrode still has a great influence on the radio frequency field homogeneity in the detective zone of the NMR spectrometer probe and provide theoretical and experimental confirmation of its electromagnetic shielding. Furthermore, we propose a novel palisade gold film device to act as the working electrode. The NMR nutation behavior of protons shows that the uniformity of the radio frequency field is greatly improved, increasing the sensitivity in NMR detection. Another advantage of the proposed device is that an external reference standard adapted to the reaction compound can be inserted as a probe to determine the fluctuation of the physico-chemical environment and achieve high-accuracy quantitative NMR analysis. A three-chamber electrochemical device based on the palisade gold film design was successfully fabricated and the in situ electrochemical NMR performance was validated in a standard 5 mm NMR probe by acquiring voltammograms and high-resolution NMR spectra to characterize the electrochemically generated species. The evolution of in situ EC-NMR spectrum monitoring of the redox transformation between p-benzoquinone and hydroquinone demonstrates the ability of the EC-NMR device to simultaneously quantitatively determine the reactants and elucidate the reaction mechanism at the molecular level.

In situ electrochemical nuclear magnetic resonance spectroscopy for electrocatalysis: Challenges and prospects

Summary Development of in situ electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy for studying electrocatalysts and associated electrocatalysis started in early 1990 s and aimed at harnessing many unique features that make NMR a ubiquitous spectroscopic method widely used in researches crisscrossing chemistry, physics and biology. Despite constant struggle with the NMR's Achilles’ heel, i.e., low intrinsic mass detection sensitivity, which is further exacerbated by the incompatibility between the electrical conduction of electrochemistry and the induction-based resonance circuitry for NMR detection, many progresses have been made in in situ EC-NMR for characterizing electrocatalysts and understanding associated electrocatalysis over the last two and a half decades. Even more exciting in the horizon is that the newly reinvigorated dynamic nuclear polarization (DPN) NMR and the fast-developing nitrogen-vacancy (NV) based, optically detected NMR, as will be discussed briefly in this Opinion, could have the transformative potential to revolutionize in situ EC-NMR to an unprecedented level.

In situ study of the magnetoelectrolysis phenomenon during copper electrodeposition using time domain NMR relaxometry.

Although the effect of magnetic field (B) on electrochemical reactions (magnetoelectrolysis phenomenon) has been long known, it has not been considered in electrochemical reactions analyzed in situ by magnetic resonance methods, such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and magnetic resonance imaging (MRI), which are intrinsically performed in the presence of B. In this report, the effect of B on the copper electrodeposition reaction, measured by a low-field (0.23 T) NMR spectrometer, was demonstrated. As expected, an enhancement in the reaction rate in comparison to the ex situ electrodeposition reaction was observed. Such enhancement was not dependent on electrodes/magnetic field orientations. Parallel and perpendicular orientations showed similar electrodeposition rates, which is explained by the cyclotron flows generated by distortions in electric and magnetic field lines near the electrode and the electrode edge. Therefore, NMR spectroscopy is not a passive analytical method, as assumed in preceding in situ spectroelectrochemical studies. Although the magnetoelectrolysis phenomenon demonstrated in this report used a paramagnetic ion, it can also be observed for diamagnetic species, since the magnetoelectrolysis phenomenon is independent of the nature of the species. Consequently, similar convection effects may occur in other electrochemical nuclear magnetic resonance (EC-NMR) experiments, such as the electrochemical reaction of organic molecules, as well as in electrocatalysis/fuel cells, lithium-ion batteries, and experiments that use electrochemical electron paramagnetic resonance (EC-EPR) and electrochemical magnetic resonance imaging (EC-MRI).

A comparative in situ195Pt electrochemical-NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials

This paper reports a detailed in situ 195Pt electrochemical-nuclear magnetic resonance (EC-NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt : Ru = 1 : 1 and were supported on carbon nanocoils and carbon black (Vulcan XC-72) respectively. The particle sizes of the two samples were determined by X-ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively- and spatially-resolved local Pt atomic fractions in the particles were deduced by using a Ruderman-Kittel-Kasuya-Yosida (RKKY) J-coupling-based method as a function of different electrode potentials. The results indicated that both samples had Pt-enriched cores and Pt-deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially-resolved Fermi level local densities of states (E(f)-LDOS), which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro-oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers.

CO surface diffusion on platinum fuel cell catalysts by electrochemical NMR

We report on surface CO diffusion processes in relation to properties of nanoparticle Pt and Pt/Ru fuel cell catalysts. The CO ad diffusion was studied by the use of 13C electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy. Measurements were carried out in the temperature range 253–293 K, where the solution side of the nanoparticle–electrolyte interface is liquid, in contrast to previous measurements, in ice. We offer a concerted view of the effect of particle size and surface coverage on CO ad diffusion, and find that both are important. We also found that the diffusion parameters were influenced by the variations in the distribution of chemisorption energies on particles of different sizes, and by the CO–CO lateral interactions. On all Pt nanoparticle surfaces investigated, we conclude that CO surface diffusion is too fast to be considered as the rate-limiting factor in methanol reactivity. The addition of Ru to Pt increases the surface diffusion rates of CO, and there is a direct correlation between the Fermi level local density of states ( E f-LDOS) of the 2π* molecular orbital of adsorbed CO and the activation energy for surface diffusion. These results are of interest since they improve our knowledge of surface dynamics of molecules at electrochemical interfaces, and may help to formulate better models for the electrooxidation of adsorbed CO on nanoparticle surfaces.

Determination of Lithium-Ion Transference Numbers in LiPF6–PC Solutions Based on Electrochemical Polarization and NMR Measurements

The electrolyte plays an important role in governing the performance of Li-ion batteries. To understand more about the role of the electrolyte, transport properties such as the lithium salt self-diffusion coefficient and the lithium-ion transference number need to be measured. In this study, the diffusion coefficient was determined by pulsed field gradient nuclear magnetic resonance (NMR). The lithium-ion transference number was determined by an electrochemical polarization method and also calculated on the basis of diffusion coefficients, which were obtained by NMR measurement, of and in the solutions of in propylene carbonate. The lithium-ion transference number and the diffusion coefficient were found to be strongly dependent on the concentration.

Coverage Dependence of CO Surface Diffusion on Pt Nanoparticles: An EC-NMR Study

We have studied the effects of CO surface coverage on the diffusion rates of CO adsorbed on commercial Pt-black in sulfuric acid media by using 13C electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy in the temperature range 253−293 K. The temperature range chosen for these measurements was such that the electrolyte is in a liquid-like and liquid environment. For CO coverage between θ = 1.0 and 0.36, the CO diffusion coefficients (DCO) follow a typical Arrhenius behavior and both the activation energies (Ed) as well as the pre-exponential factors ( ) show CO coverage dependence. For partially CO covered samples, Ed decreases linearly with increasing CO coverage, indicating that the repulsive CO−CO interactions exert a stronger influence on the coverage dependence of the activation energy than does the nature of the CO adlayer structure. On the other hand, shows an exponential decrease with increasing CO coverage, consistent with the free site hopping model [Gomer, R. Rep. Prog. Phys. 1990, 53, 917] as the major mechanism for surface diffusion of CO at partial coverages, unlike the situation found with a fully CO covered surface [Kobayashi et al., J. Am. Chem. Soc., 2005, 127, 14164]. Overall, these results are of interest since they improve our understanding of the surface dynamics of molecules at electrochemical interfaces, and may help facilitate better control of fuel cell reactions in which the presence of surface CO plays a crucial role in controlling electrocatalytic reaction rates.

Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study

Oxygen reduction reaction (ORR) measurements and (195)Pt electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy were combined to study a series of carbon-supported platinum nanoparticle electrocatalysts (Pt/CB) with average diameters in the range of roughly 1-5 nm. ORR rate constants and H(2)O(2) yields evaluated from hydrodynamic voltammograms did not show any particle size dependency. The apparent activation energy of 37 kJ mol(-1), obtained for the ORR rate constant, was identical to that obtained for bulk platinum electrodes. Pt/CB catalysts on Nafion produced only 0.7-1% of H(2)O(2), confirming that the direct four-electron reduction of O(2) to H(2)O is the predominant reaction. NMR spectral features showed characteristic size dependence, and the line shapes were reproduced by using the layer-deconvolution model. Namely, the variations in the NMR spectra with particle size can be explained as due to the combined effect of the layer-by-layer variation of the s-type and d-type local density of states. However, the surface peak position of (195)Pt NMR spectra and the spin-lattice relaxation time of surface platinum atoms showed practically no change with the particle size variation. We conclude that there is a negligible difference in the surface electronic properties of these Pt/CB catalysts due to size variations and therefore, the ORR activities are not affected by the differences in the particle size.

Coverage Dependence of CO Surface Diffusion on Pt Nanoparticles - an EC-NMR Study

AbstractWe have studied the effects of CO coverage on surface diffusion rates of CO adsorbed on nanoparticle Pt catalysts in sulfuric acid media by using 13C electrochemical nuclear magnetic resonance spectroscopy (EC-NMR) in the temperature range 253 - 293 K. For CO coverage from θ = 1.0 to 0.36, the diffusion coefficients follow Arrhenius behavior and both activation energy (Ed) and pre-exponential factor (Dco) show CO coverage dependence. Ed increases from 6.0 to 8.4 kcal/mol and DCO varies from 1.1 X 10-8 to 3.7 X 10-6 cm2/s when the coverage is increased from θ = 0.36 to θ = 1.0. On the Pt catalyst surface at partial CO coverage, our data strongly support the free site hopping model of adsorbed CO as the major surface diffusion mechanism, unlike the situation found with a fully CO covered surface where CO exchange between different surface sites is believed to be the major diffusion mechanism. Our results also indicate that the contributions of lateral repulsive interactions exert a stronger influence on the diffusive motion than does the nature of the surface structure. When the diffusion coefficient was estimated from CO stripping measurements by using an electrochemical modeling protocol, the estimated diffusion coefficients were a few orders of magnitude larger than those obtained from the EC-NMR experiments. Overall these results are important for improving our understanding of electrochemical surface dynamics of molecules at interfaces, and may help facilitate better control of fuel cell reactions where the presence of surface CO plays a crucial role in controlling the reaction rates.